1. Field of the Invention
The present invention relates to a process for producing a polyphenol diester (hereinafter simply referred to diester) by esterifying a polyphenol compound having 2 to 10 phenolic hydroxyl group and having a molecular weight of equal to or less than 1,000 with a naphthoquinone-1,2-diazidesulfonyl halide. It also relates to a positive photosensitive composition using this diester.
2. Description of the Related Art
Positive photoresist compositions each comprising an alkali-soluble resin and a quinonediazide group-containing compound (photosensitizer) are excellent in definition, sensitivity and etching resistance and hence have been used for the production of semiconductor devices and liquid crystal devices.
Photosensitizer used in such positive photoresist compositions can usually be obtained by esterifying a polyphenol compound having 2 to 10 hydroxyl groups and having a molecular weight of equal to or less than 1,000 with a naphthoquinone-1,2-diazidesulfonyl halide.
These conventional photosensitizers, however, comprise different types of esters (e.g., monoesters, diesters and triesters) and hence may respond to light unequally or have a deteriorated contrast.
Japanese Patent Laid-Open No. 2-19846 discloses a positive photoresist composition which employs a photosensitizer comprising more than 50% of a diester relative to quinonediazidesulfonic esters of a phenol compound. This conventional technique may provide a high definition since the photosensitizer contains a large proportion of the diester, but it requires the use of a halogen-containing solvent such as chloroform, trichloroethane, trichloroethylene and dichloroethane and such a solvent adversely affects the environment. The literature also refers to the production of a diester in the presence of triethylamine, but such a diester as produced in the presence of triethylamine cannot provide an intended definition and exposure margin, as described in detail below.
Japanese Patent Laid-Open No. 6-167805 and No. 8-339079 each discloses a photosensitizer comprising an increased proportion of the diester. These techniques, however, require the use of polyphenol compounds each having a specific skeleton, and they cannot be applied to any other polyphenol compounds than the specific polyphenol compounds.
Japanese Patent Laid-Open No. 7-261382 discloses a technique of increasing the proportion of a diester by using a basic catalyst such as alicyclic amines including, for example, 4-methylmorpholine, N-methylpiperazine and N-methylpiperidine. The basic catalysts used in this technique are different from those of the present invention, and in addition, the technique also requires the use of polyphenol compounds each having a specific skeleton and cannot be applied to any other polyphenol compounds.
In addition, as the basic catalysts, there are known ethylamine, ethanolamine, diethylamine, diisopropylamine, diethanolamine, dicyclohexylamine and other primary or secondary amines, and trimethylamine, tripropylamine and other tertiary amines each having a lower alkyl group. With any of these basic catalysts, however, a diester cannot be selectively produced from any of various polyphenol compounds.